In a scientific first of its kind in the history of modern astronomy, a team of Chinese scientists succeeded in achieving a major accomplishment by deciphering the mysteries of one of the most mysterious celestial objects, as they were able to make the first direct and accurate measurement of the mass of a “free-floating planet”, confirming that it is a planet with a mass similar to that of Saturn.
The results of this groundbreaking research, led by a specialized team from the Department of Astronomy at the School of Physics at Peking University, have been published in the prestigious journal Science, lending high global credibility to this discovery that could change our understanding of the formation of planetary systems.
What are free-floating planets?
To understand the significance of this event, we must consider the broader context of these objects. Free-floating objects, sometimes called "rogue planets," are celestial bodies that do not orbit any host star, but rather wander alone in the darkness of interstellar space. Over the past decade, nearly a dozen such objects have been discovered through ground-based telescopes. However, scientists have faced a significant challenge in accurately measuring their masses because there is no star they orbit that can be used as a reference point for calculating gravity and mass using traditional methods.
Gravitational microscope lens technology
The head of the research team, Dong-Soo Poh, explained the complex mechanism used in this discovery. When a free-floating object passes in front of a distant background star, the object's gravity acts as a magnifying lens, bending the star's light towards us. This causes the star to light up and brighten temporarily, a physical phenomenon predicted by general relativity and known as a "microlensing event".
In 2024, the team observed a remarkable microlensing event using both ground-based and space-based telescopes simultaneously. The brilliance of this achievement lies in overcoming a physics problem known as "mass-distance decay," where it is usually difficult to distinguish between a small, nearby object and a large, distant one using a single observation. However, by combining observations from Earth and a distant spacecraft with a precise time lag, the scientists were able to extract distance information from the object using the technique of parallax, and then determine its mass and distance separately and with exceptional accuracy.
The importance of the discovery and the future of astronomical observation
The significance of this achievement lies not only in determining the planet's mass, but also in its potential to serve as a pivotal reference point for the future of space exploration. As one reviewer in the journal Science commented, this research highlights the immense advantages of coordinated observations between space and Earth.
This success provides a roadmap and an important reference for upcoming mega-projects, such as NASA’s Nancy Grace Roman Space Telescope, which aims to conduct a comprehensive survey of exoplanets. The ability to measure the masses of these wandering objects will help scientists understand how these planets were ejected from their parent solar systems, or whether they formed independently like stars, opening new avenues for understanding galactic dynamics.
